A common practice in manufacturing products containing fibrous material, such as manufacturing mats or packs of mineral material, is to apply a binder material to the fibers, thereby connecting the fibers with each other and giving structure and resiliency to the product. In the manufacture of mats of mineral fibers, a preferred binder is an organic binder, such as a phenol-formaldehyde urea binder. Phenol-formaldehyde urea binders have been found to be particularly useful in the manufacture of glass fiber mats for such uses as insulation products.
In the manufacture of mineral fiber mats having a binder thereon, it is usually necessary to subject the mat and binder to a curing oven to advance the binder to a cured or set state. One off the problems associated with passing mineral fiber mats through curing ovens is that there is a certain lack of control over the process, i.e., the product is often either undercured or overcured. Attempts have been made to measure, during the production process, the amount of binder on the mats and the extent to which the binder has been cured, but previous attempts were not sufficiently accurate for process control purposes.
A previous method for measuring characteristics of a mat of fibers as disclosed in U.S. Pat. No. 4,363,968, to McGowan et al., including radiating the mat with electromagnetic radiation having different wavelengths with each wavelength being absorbed (or not absorbed) by various components of the mat and binder. By choosing infrared radiation which is absorbed by the binder, and measuring the transmission of the radiation through the pack, an indication of the amount of binder present is obtained. In practice, two wavelengths of infrared radiation have been used, one which is absorbed by the binder and one which is unaffected by the binder. Taking the ratio of the two gives a signal related to the binder content. For example, a first energy which is absorbed by the binder and a reference energy, which is not absorbed by the binder, could both be directed toward the mat. A simple comparison of the sensed energies transmitted through the mat and the binder would disclose the relative amount of the first energy absorbed and thereby disclose the amount of binder on the mat.
Such a prior art method is deficient, however, in that the amount of the energy absorbed by the binder is not only a function of the amount of binder present within the pack, but also upon the degree of cure or advancement of the organic binder toward a cured state. It is not always possible to find an energy with a wavelength which is insensitive to the degree of cure. Thus, there is a need for a method for measuring binder characteristics in a mat of binder-coated mineral fibers which takes into account the effect of the degree of cure on the measurement of the amount of binder in the mineral fiber pack.